The present invention relates to thermal processing of items in a continuous process, especially food products. The invention relates to a chamber and a method for heating or freezing food products by a combination of thermal conduction between a conveyor belt and the product and thermal convection between a cooling or heating medium and the product. The combination provides a better product quality and a higher capacity of the chamber.
Devices and methods for continuously freezing or heating food products e.g. for form freezing the food products exist. Known devices typically have conveying means for conveying the food products through either a heating or a freezing process. The conveying means are typically provided as conveyor belts with an open structure allowing either a cooling or a heating medium such as air to pass through the belt. The belts therefore have conveying surfaces which are non-uniform or rough and which typically causes unwanted structures in the food products as they are either heated or frozen while being supported on the surface. Furthermore the non-uniformity gives a poor thermal conduction from the surface of the conveyor belt to the food products and therefore the thermal efficiency of the devices is relatively low.
When sensitive or delicate food products, such as fish fillets are individually frozen, it is neccesary that the products obtain a stiff outer shape before the product is being handled further, otherwise the value of the product may be lowered. It is therefore essential that the form freezing of the products is completed in one process. In order to ensure the form stability the known tunnel freezers or IQF (Individual quick freezer) installations have relatively long form freezing conveyor belts and therefore the known freezers take up relatively much space. The same problem applies for devices for continous heating such as for conveyor ovens.
The known devices typically use conveyer belts wherein a cooling or a heating medium is blown onto the food items either from the side of the belt or from above the belt. Sufficient cooling or heating is achieved by extending the length of the conveyer belts and thereby the size of the chamber. This can be a problem e.g. when the chamber is installed in ships or in other places with limited space.
It is an object of the present invention to provide a method and a device for continuously processing sensitive food products wherein the efficiency of the processing is improved so that the quality of the product can be improved with the use of less space for the device.
One object of the present invention relates to a thermal processing chamber for processing individual product items, said processing chamber comprising:
a conveyor for conveying the product items in the chamber, said conveyer comprising:
a conveyor belt forming an endless loop with a processing part and an idling part, the conveyor belt comprising a plurality of thermal conductive elements, each of the elements being adapted to obtain a first orientation in the processing part of the loop and adapted to obtain a second orientation in the idling part of the loop, the first orientation providing a substantially plan and continuous surface for supporting the product items across at least a number of the elements, and
power driven means for advancing the conveyor belt,
wherein the thermal processing of the product items is performed by a thermal conduction from the elements to the product items.
The power driven means could be regular AC/DC motors with a control system adapted for controlling the position and speed of the conveyor belt. The control system could be integrated in an industrial PC, which could also be used for the control of the chamber in general, e.g. for the control of the temperature of the chamber or for the control of the processing of the product items.
The chamber may further have means for providing a thermal media to the chamber. The thermal media could be a gas such as plain air, which is either relatively hot or cold.
The second orientation of the elements could preferably be adapted so that a passage is provided between the elements. This will allow the cold or hot air to flow between the elements and thereby ensure a good distribution of the cold or hot medium in the chamber. At the same time it will allow the medium to cool the elements down or heat them up before they re-enter the processing part of the loop. Preferably the second orientation is adjustable so that the size of the passage can be adjusted, e.g. so that the amount of gas flowing between the elements can be controlled.
The thermal conductive elements could be parallel arranged elongated beams having a wing formed cross sectional shape. By arranging each of the beams pivotally around a longitudinal centre axis of the beams, the first orientation of the beams may provide a flat and continued surface across a number of the beams. The second orientation of the beams may provide an open structure with good conditions for the flow of the medium between the beams.
The thermal processing of the product items is preferably performed as a combination of a first thermal conduction between the elements and the product items and a second thermal convection between the thermal media and the product items.
The elements could be thermally influenced by a thermal convection between the thermal media and the elements or the thermal media could be influenced by a thermal convection from or to the element. As an example the elements could be either cooled down or heated up with cold or hot air flowing in between the elements or the air flowing in between the elements could be either heated or cooled down by the elements. The one or the other situation could be selected based upon which heating or cooling procedure that would be beneficial for a specific case. In a regular cooling process it would make most sense to let the elements be cooled down with cold air produced in a regular cooling element, e.g. comprising a compressor and an evaporator. In a regular heating process on the other hand, it may make more sense to let the air be heated as it passes the elements, which are heated, from internal electric heating elements.
According to one embodiment of the invention the thermal processing is freezing of the product items and accordingly the thermal media is a cooling media, which could be selected from a group comprising:
plain air,
CO2 and
nitrogen.
The elements could also cooled electrically, e.g. by internal thermoelectric elements.
According to another embodiment of the invention the thermal processing is heating and accordingly the thermal media is heated gas such as heated air. The air could be heated in a heat exchanger or the air could be heated by the elements, which again could be heated by internal electric heating elements.
Preferably the elements are made from a material with a good thermal conductivity such as aluminium. It has been found that a conductivity between 30 W/(K*m) and 230 W/(K*m), such as between 209 W/(K*m) and 229 W/(K*m) is preferred in order to obtain an efficient cooling or heating of the product items positioned on the elements. W is the conducted energy, K is degrees Kelvin and m is the length of the material.
The elements could be coated with a material with a low surface friction for the working temperature. As an example the elements could be coated with PTFE (Teflon(trademark)) or a similar plastic material. The coating enables the products to fall off the conveyor at the end of the processing part of the loop, and not stick to the surface of the elements after either a freezing of the products or after a heating of the products. The coating could further protect the elements from corroding. Preferably the elements or the beams are made from deep drawn aluminium profiles which after a chemical sintering is coated with Teflon(trademark).
The elements could be adapted to rotate from the first orientation to the second orientation upon movement of the elements in the endless loop from the processing part to the idling part of the loop. The rotation could be caused by gravity in that the elements or beams simply falls from the first orientation around a pivotal hinge into the second orientation. The elements could then be adapted to rotate back from the second orientation to the first orientation upon movement of the element in the endless loop from the idling part to the processing part of the loop. The rotation could again be caused by gravity in that the elements and the beams are rotating as they are raised vertically in a circular movement, e.g. around a support or driving wheel of the conveyor. The rotation of the elements or beams could be stopped in the second orientation wherein the elements or beams are supported, e.g. by the succeeding element or beam in the loop.
The thermal chamber may be provided with a number of additional conveyors. The additional conveyors could be provided with belts having a partly open surface towards the thermal media. As an example the belts can be regular plastic belts with a 20, 30 or even 40 percent open structure allowing the thermal media to path through the belts. Such belts would not support thermal conduction directly between the belt and the product items but would allow the thermal media to flow through the belt and therefore support the convection between the thermal media and the product. The convection between air and the product would not be as effective as conduction directly between a belt and a product fully supported on the surface of the belt. Still the convection is relatively effective in the case where the products are not lying firmly against the surface of the belt anyway and that would typically be the case after the products have been thrown from one belt to another. The plastic belts or similar regular belts can be used e.g. to full freeze the products by convection between the air and the products.
According to a preferred embodiment of the invention the product items are food items such as fish, meat, cake, bread etc. Accordingly the materials selected for the chamber should be adapted for the purpose of hygienic treatment. Typically the extensive use of non-corrosive materials such as stainless steel and plastic would be preferred.
Another aspect the invention relates to a method of thermally processing product items in a thermal processing chamber provided with a thermal media, said method comprising the steps of:
conveying the product items through the chamber on a plurality of thermally conductive elements,
thermally processing the product by providing a thermal conduction between the elements and the product items, and
simultaneously providing a thermal convection between the thermal media and the product items.